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TVS Working Principle

TVS (Transient Voltage Suppressor) is an integrated device of a single PN junction or multiple PN junctions fabricated by the semiconductor diffusion process. TVS can be divided into two types, including unidirectional TVS and bidirectional TVS. Unidirectional TVS is generally applied to DC power supply circuits and bidirectional TVS is applied to circuits with an alternating voltage. In the DC circuit, the unidirectional TVS is reversely parallel to the circuit. When the circuit is working normally, TVS is in the off state (high-impedance state) and it won’t affect the normal operation of the circuit. When an abnormal overvoltage occurs in the circuit and reaches the TVS (avalanche) breakdown voltage, TVS will change from the high impedance state to the low impedance state rapidly, discharging the transient over current caused by the abnormal over voltage to the ground. Besides, the low clamping voltage between both ends of the PN junction will be maintained, thus preventing the circuit of the post-stage from damage caused by the abnormal overvoltage. When the abnormal overvoltage disappears, the resistance of TVS will return to the high impedance state.

DOWOSEMI supplies TVS products:
·DO-218AB：SM5S、SM6S、SM8S、SM8SxxCA；
·SMA/DO-214AC：SMAJ、P4SMA、TPSMAJ、SMA6J、TPSMA、SACA；
·SMB/DO-214AA：SMBJ、P6SMB、TPSMBJ、SMB10J、SACB、1.0SMB、TPSMB；
· SMC/DO-214AB：1.5SMC、SMCJ、TPSMCJ、SMDJ、TPSMDJ、5.0SMDJ、TP5.0SMDJ、TPSMC；
·SOD-123：SMF、TPSMF、SMF4L、SMF3.3A、SMF3V3A；
·DO-41：P4KE;
·DO-15：SA、P6KE、SAC；
·DO-201：1.5KE、LCE；
·R-6/P600：3KP、5KP、LDP、15KP、30KP；
·NA：KA

TVS Features

·Made by semiconductor technology, with high reliability, no damage limit;
·Glass passivation process, precise on-off voltage;
·High transient power, low capacitance, low leakage current, easy to control clamping voltage;
·Very fast response time:usually less than 1.0ps;
·Excellent clamping ability, small deviation of breakdown voltage;
·High voltage precision. In special applications, through the process or parameter screening can achieve higher precision;
·Small size, easy to install;
·Uni-directional and bidirectional units;
·200W-30000W or even higher peak pulse power capability with a 10/1000μs waveform, repetitive rate (duty cycle):0.01 %;
·Working voltage:3.3V-600V, or even higher;
·Diversified packaging forms: SOD-123、SMA /DO-214AC、SMB/DO-214AA、SMC/DO-214AB、DO-218AB、DO-41、DO-15、DO-201、R/P-600, etc.;
·Halogen-free, RoHS compliant;

TVS Selection Guide

1)To determine the maximum DC or continuous working voltage in the protected circuit, the rated standard voltage and "high end" tolerance of the circuit;
2)The rated transient power of TVS is greater than the maximum transient surge power that can occur in the circuit;
3)The cut-off voltage of TVS should be greater than the maximum operating voltage of the circuit being protected;
4)The maximum clamping voltage of TVs is less than the damaged voltage in the protected circuit of the later stage;
5)After the TVS maximum clamping voltage is determined, the peak pulse current is greater than the transient surge current;
6)For the circuit protection of data interface, it is also necessary to select TVS with appropriate capacitance. For example: when the signal frequency or transmission rate is higher, TVS with low junction capacitance series should be selected;

TVS Parameters

· V_RWM: Cut-off voltage, the highest operating voltage of TVS, the maximum dc or ac peak voltage that can be continuously applied without causing the deterioration or damage of TVS. Under VRWM, TVS doesn't work.
·V_C: Clamp voltage, the peak voltage measured at both ends of TVS when the peak pulse current IPP of the specified waveform is applied.
·V_BR: Breakdown voltage is the minimum avalanche voltage of TVS. Refers to the voltage measured at the two ends of TVS on the v-i characteristic curve under the specified pulsed dc current IT or current close to avalanche.
·I_R: Leakage current, also known as standby current. Under the specified temperature and maximum working voltage, the maximum current flowing through TVS is measured at the cut-off voltage.
·I_PP: Peak pulse current, usually the peak under the current waveform of 10 / 1000 μs.
·I_T: Test current.
·C: Capacitance value. For TVS at the same power level, the lower the voltage, the greater the capacitance. In the protection of communication lines, especially attention to the capacitance value of TVS.
·Encapsulation: According to the encapsulated form of TVS, we can see the power. The chip area of TVS directly determines its power level.

TVS selection Matter

1)The specification manual only gives the peak absorption power under a specific pulse width, while the pulse width in the actual circuit is variable.
2)For the protection of small current load circuit, the current limiting resistance should be increased consciously.
3)Pay attention to that the steady-state average power of TVS is within the safe range.
4)Consider temperature changes. Under normal conditions, TVS operates between - 55 ° C and 150 ° C. If the temperature in the circuit is high, it should be reduced.
5)The lead length of TVs shall be opposite to the protected line.
6)For protection in data interface or communication line, TVS with relatively small capacitance value should be selected as far as possible.
7)Uni-directional TVS is applied for DC protection circuit, bidirectional TVS is applied  for AC protection circuit, TVS array device is applied for multi-path protection circuit, and special protection module is applied for high-power protection circuit.
8)In using TVS, minimize the number of strings/unions, given the discretization of TVS.

TVS Application

Due to its advantages of extremely fast response speed, low clamp voltage, and accurate voltage, TVS is applied in fields with high requirements for protection devices, such as automotive electronics、home appliances、industrial control、 lighting、communication and medical industries, such as DC power cord、RS-485 interface、communication power supply、I/O port、 etc.

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